Can' add TXT record (bigger than 255 bytes) in PowerDNS

Hi , I want to set up DKIM on my email server. For that I need to add a TXT record on my pdns server.I can't do this on EasySCP web interface , I try with pdnsutil edit-zone but I can't add more than 150 characters in first phase. I try to edit in pma the [Blocked Image: http://10.0.0.19:8081/pma/themes/dot.gif]Database: powerdns »[Blocked Image: http://10.0.0.19:8081/pma/themes/dot.gif]Table: records - > content and I put 256 in Length/Values field (max. admited) , and after that ,I can put a max 256 char TXT record in pdns. Although various RFC and forums say that we can concatenate strings of text , gen
IN TXT "string1" "string2" , for a TXT record bigger than 256 this is not work for me.

Error in pdnsutil edit-zone was and is :Error: Parsing record content (try 'pdnsutil check-zone'): Data field in DNS should end on a quote (")...... if I try to put IN TXT "string1" "string2 record . The editor delete the last quota , probably (I am pretty sure) the length of string. The same thing is happened when I try to edit the record with pma (no more 256 characters , no matter if I try to concateneted or not).